While this question surely has pretty broad relevance, it comes to mind right now pertaining to a specific vehicle: my 1997 Mazda B2300, 187,000 miles. The truck is on its second battery; the factory unit lasted almost exactly five years before dying, and the current one is about four years old. As suggested by my location field, this vehicle spends its time in a relatively warm climate. At present there is no indication of trouble with the battery, alternator, or anything else, but the battery is getting a bit long in the tooth.
I could simply replace it now and be done with it (on my timetable rather than Murphy’s). I might do that regardless of the responses I get here, but that won’t do anything to dispel my ignorance - so I’ll go ahead and ask the question that’s rattling around in my skull:
Many auto parts stores offer free battery checks, performed (IME) by an employee who may or may not really know what he/she is doing. Is such a test simply thumbs-up or thumbs-down on the battery, or can it give some kind of feedback on how much more “life” remains in the unit?
Would I be likely to learn anything useful by getting my battery tested?
Yea, I’ve seen those battery testers at the auto parts stores. I’m not sure if they properly test a battery. And like you, I don’t have much confidence that the sales dude knows anything about batteries and how to test them.
If your battery seems to be working, I wouldn’t do anything.
Crafter_Man, how would you test a car battery? I’m not asking how the parts stores do it, but rather what would be a good test?
I don’t think voltage would necessarily be a good indication, and you wouldn’t want to significantly discharge the battery, would you? I’ve heard that’s not good for car batteries. So would you test the amperage the battery can provide? Just curious.
The classic method of determining a batteries strength is to use a hydrometer to check the electrolyte in each cell. I must confess that I don’t know how to do this w/ the newer sealed batteries.
If it’s a serviceable battery, remove the vent caps and test the specific gravity of the electrolyte fluid. A tester for this is pretty inexpensive ($5-10?). A difference of 30 points between any cells is suspect, a difference of 50 is bad (replace now). If there’s not enough liquid in the cells to fill the tester, bring them up to their full mark with clean water and wait a day or two for it to mix in. If the liquid is below the metal plates inside, buy a new battery now.
Other tests require pricier equipment or trickier procedures. A load test can be done with a load tester, or by disabling something to prevent the engine starting and then cranking it for 10 seconds, in either case reading the battery voltage at the point it’s been under load for 10 seconds. Starting with a fully charged battery (12.6 v), it should read at least 9.8 v for the load test - but if it’s close to that, it’s weak. Really good batteries read over 11 v.
The fancy (and expensive!) electronic testers measure capacitance. I’m not terribly familiar with them, and I don’t know if they indicate a degree of health or just pass/fail.
Basically, you don’t. In some cases, you might be able to break off the vent caps and access the cells, but then you’ve affected the mechanism that makes them maintenance free. Hence the dependence upon electronic testers nowadays.
A load test is also a long-used classic procedure, and can be done on any battery.
A “good” test would measure the internal resistance of the battery. This is done by measuring the battery voltage as a function of current. The less the voltage drops with increasing current, the lower the internal resistance is, and the healthier the battery is.
Start with a fully charged battery. This means using 2 - 4 amperes overnight charging.
Allow the battery to sit (or rest) without discharge or charge for between six to twelve hours at room temperature, if possible, to allow for the surface charge to dissipate. (Recommended method.)
Turn the headlights on high beam for five minutes, turn them off, and wait ten minutes.
With a battery load tester, apply a load at one-half the battery’s CCA rating for 15 seconds and then wait ten minutes.
Disable the ignition, turn the engine over for 15 seconds with the starter motor, and wait ten minutes.
Apply a load that is 33% of the ampere-hour capacity for five minutes and wait ten minutes.
4.3.6. With a battery load tester, apply a load is one third the battery’s amp-hour rating for five minutes and wait five minutes.
You should read 12.6 volts or better after the “load test” or whatever method you use. For everything you need to know about auto and marine batteries see
Most of what you posted is either incomplete or misleading.
Ah wouldn’t just driving the car do just as well? If the charging system is not keeping your battery fully charged, this is a major problem, and will be discovered by doing a thorough battery/starting/charging system test.
Removing surface charge is only necessary if you are trying to measure open circuit voltage. Open circuit voltage is just one test (and a very rudimentary test at that) for a battery
What you have just almost described is a battery load test. There are two problems with removing surface charge this way. First off it requires a very expensive piece of test equipment. Secondly why would you not just read the voltage loaded at the end of the 15 seconds? Then you would have preformed a battery load test, which is a much more comprehensive test than OC voltage.
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Disable the ignition, turn the engine over for 15 seconds with the starter motor, and wait ten minutes.
these will remove surface charge. So will turning on the headlights for 30 seconds. Just how are you going to apply a 33% load, I wonder? Turning on the key and headlights for 30 seconds is a lot easier IMHO
One third = 33% where I went to school, this is the same as the previous sentence.
None of the tests described are a load test. All you have described is ways to remove a surface charge. A load test is a very specific that is done with a variable load carbon pile tester like the one I linked above. These are professional grade pieces of equipment and not often found in a homeowner’s garage.
There are 4 basic tests that can be done easily on an automotive battery. Two of them require expensive pieces of equipment, two do not.
Open circuit Voltage test
Equipment needed: Digital voltmeter $10 and up
How: Remove surface charge, either by parking the car overnight, or turning on the key and headlights for 30 seconds. If you use the headlights, go drink a cup of coffee before doing the test. Red lead to positive, black to neg. Read voltage.
Test results: Above 12.6V battery if fully charged. You don’t know dick about if it will start your car tomorrow AM, but it is fully charged. There is a difference between state of charge and capacity.
What to do if the test result is bad Charge battery at a low rate (<5A) overnight and retest. Remove surface charge and retest. If voltage is still low, replace battery
**Hydrometer ** NOTE: This test is not possible on sealed batteries.
Equipment needed Hydrometer, about $20 Get the kind with that reads specific gravity, not the floating ball kind.
How Remove cell caps, suck up enough electrolyte from the first cell to make the float float. Read the SG on the side of the float. Correct for temp. Write down your corrected reading. Lather, rinse, repeat for the remaining cells.
Test Result Fully charged battery should be a SG of 1.265. All cells should be within 30 points (0.030)
What to do if the test result is bad All cells low? recharge and retest. Still Low? Is the Open Circuit voltage OK? Then you have a bad hydrometer. One cell low? More than 50 points = replace battery. More than 30 less than 50 points? How lucky do you feel? You can try recharging, but you will probably wind up replacing the battery.
Now we get to the spendy stuff Conductance testing
Equipment needed A conductance tester While these are kind of spendy, these are what most auto parts stores and many shops use now for testing batteries. Often these tests are free at places that sell batteries.
How Tester is hooked up pos and neg. User inputs CCA rating of battery, in/ out of car, and presses test button. unit measures conductance of the battery and renders a decision in 15 seconds.
Test Result(s) Good may include state of charge, and actual cold cranking amps available
What to do if the test result is bad bad, charge and retest. Bad = replace battery. Charge and retest? do what it says.
Note: very fool proof testing. The only chance for user error is an incorrect CCA input. Used by many car makers for battery warranty decisions. Here is a PDF telling you about these testers.
Load test
Equipment needed Variable Carbon pile tester Very spendy
How Battery must be above 75% state of charge to start. Tester is hooked up, and a load equal to either 1/2 of the CCA or 3X the AH rating of the battery is applied to the battery for 15 seconds. At the end of 15 seconds voltage is read with the load still applied
Test Result Above 9.6V at 70F battery is good. Add 0.1V for every 10F above 70, subtract 0.1V for every 10F below 70F. A real strong battery will hold above 10V during this test.
What to do if the test result is bad If battery was not at 100% state of charge, you can try a charge and retest, but you will probably just replace the battery.
Note: In the hands of an experienced operator, a variable carbon pile tester is the standard to which others testing methods are measured. However in the hands of an inexperienced operator, the results will be garbage.
Getting back to the OP, If it were me, I would either take my car to an auto parts store that offers free testing on batteries using a conductance tester, or Sears used to offer a very comprehensive battery /starter/charging system test. Computerized and very well done in my professional opinion.
I don’t know the cost, I saw it when I went to warranty a battery for a friend.
I’d do that if I were you too. The OP wanted a quick and dirty test for the battery, after 4-5 years the smart thing to do is replace it. Sorry if you’re unclear on that.
Sorry if he’s unclear on that? WTF? I don’t see where Rick is unclear on anything.
You, on the other hand, have posted a needlessly varied list on removing surface charge, which is not a load test as you imply, and which is quite irrelevant to the question at hand.
And that question is not “what’s a quick and dirty test for a battery,” it’s “Would I be likely to learn anything useful by getting my battery tested?” - which question Rick has addressed by listing the types of tests available and the significance of the results.
I purchased a LoadTester (130A) at Sears for $59… (I have a boat and 4 batteries in it, as well as the cars, so taking them to a shop for testing is a PITA).
I unhooked the charger(s) and waited most of a day… is that sufficient in most cases to remove the surface charge?
I then proceeded to test the batteries (3 in series, 1 Isolated) with the load tester… load tester never went below 12v, and I hit each of the deepcycles atleast twice concurrently (1 test, waited a few seconds, did another test)…
Was taht a sufficient test? Or did I miss something?
I’d say you’re okay. That type of load tester has a single preset load, as opposed to the variable load of a carbon pile tester, which means it can’t test as accurately for different CCA ratings of different batteries. Nevertheless, it’s sufficient to do the job in most cases, especially if the operator understands its limitations and adjusts for them (as you did in repeating the tests). Actually I’m surprised nothing went below 12v - the car batteries I test always do (I read the voltage with DMM, not the tester’s built-in meter).
The day’s wait should have been enough to dissipate surface charge. The first load test certainly was.
I’ll go ahead and get it tested. It sounds like conductance testing can tell one that a battery has started down the path to ruin, but even the Midtronics PDF Rick linked hedges a bit on trying to predict remaining life (understandably). Perhaps the best thing would be to routinely test batteries every year or so, just to get a feel for the baseline result of such a test?
I don’t want to replace a perfectly serviceable battery “just because”, but in my experience one gets very little warning when a battery fails in service. Fine on Monday, slight hesitation starting on Tuesday, followed by can’t-get-to-work on Wednesday. Hopefully this test will allow me to make a more educated decision on whether or not to risk going longer with the present battery - and it sounds as if it should (which was really the info I wanted when I started this thread).
Yes that would be sufficient to remove the surface charge.
Ah I’m not trying to pick on you, but I think you mean the three batteries are in parallel not series (unless your boat has a 36 volt system)
If you left the three batteries hooked in parallel, and hit them with a 130A load I would be very susprised if the voltage ever got anywhere near 12 Volts.
::: does a quick google on deep cycle marine batteries:::
If you had 3 of these bad boys in parallel you would have 2,535 cold cranking amps. Your 130 Amp test would be a fart in a whirlwind to that kind of power.
Isolate the batteries, and retest one at a time. Depending on the CCA of your batteries you might have to repeat the test several times to get some indication of true battery condition.
I am not a fan of fixed rate “toasters” as they give a very poor indication of true battery condition, but you seem to have a pretty good grasp of their limitations.
The Midtronics testers that we use give both a state of charge, and actual CCA available from the battery. A new battery (or fairly so) always seems to give a much higher actual CCA than rated CCA. Example a 600 CCA battery might show 740 CCA.
If you did these tests often enough (every 6 months? every year?) You could probably get a good feel for a good floor that you would not want the CCA to drop below. of course you would have to drive a battery or two till they died.
Unless you own the tester, or have a friend that is a technician, I’m not quite sure how you would go about getting this actual CCA info on a regular basis. I guess that will be left as an exercise for the student.
They are in series as I have a 36v Trolling Motor… and I do have group 27 batteries (Interstates)… I keep them on an onboard charger, and they are about 2 years old now… first time I’ve had deep cycles last me this long.
For reference, I have
On the past few trips, I didn’t feel I was getting the power I should, and I didn’t want to take them to a place that sells batteries and ask them “Do these need to be replaced?” (I have trust issues at times)… so I wanted to learn to test them myself… that and as said before, pulling and lugging 3-4 batteries in and out of the boat is a major PITA.
On my main cranking battery, I would now and then get “low voltage warnings” from some of my electronics, and I wanted to eliminate the battery as a source… so that I could focus on running new wire as needed… I’ve probably got a corroded ground running to the bow of the boat.
What I need to do now is get that Hydrometer thingy to keep up on that.
36V trolling motor, who know?
Consider my ignorance fought for the day.
Anyway I would still isolate the batteries and test them one by one.
Also do you know how to do a voltage drop test?
It will allow you to find the bad grounds/poor connections in your rig. With water around corrosion is a constant battle.
If you don’t know, I would be happy to provide instructions.
Boat manufacturers can be very stupid at times… daisy chaining the main ground between about 30 switches and devices is just plain stupid, plus they don’t plan for the extra electronics, so they didn’t use a heavy enough main power line… They used 12-14g when they should’ve used 8-10g.
This last place I see the voltage drop is to one piece of electonics (a fishfinder) at the bow of the boat… since its the only thing up there (other than the bow light) I’m just gonna run an isolated ground/power wire to it and bypass the junk that is in there… (all electronics run off of the main/cranking battery)
The load test helped me make sure the battery itself wasnt the source of the issue, since sometimes the low voltage would go away after a short run, but not for long… so, I’m thinking the ‘surface charge’ was somehow helping a corroded/loose ground seem better for a short period of time.
oh, and I did test the batteries ‘one by one’, just didn’t unhook the series… it’s my understanding that is still considered isolated as far as the test is concerned.
